The Layman's Perspective: So, why is every engine turbocharged nowadays?

Nowadays, we come across the sentence, or more appropriately, the cry of the "enthusiasts" that, the NA (Normally Aspirated) engines are a dying breed.

Expressions of shock and horror are to be heard whenever a manufacturer dumps a NA engine in the favour of turbocharged/supercharged engine. The collective whining of the so called 'NA Purist' reached a peak when BMW M launched their first ever turbocharged M engine - the S63Tü. Obituaries began to be written about M and how it was only a matter of time before the M division, as we all had come to know, ceased to exist. And so on....

Firstly, let's tackle the emotional aspect of this situation. Why are NA engines so highly revered by the majority of the "purists" , "enthusiasts"? The answer is simple - Just listen to a 458 Italia singing at 9000rpm's compared to a Nissan GTR-R35 buzzing at 6000/7000rpm's. Both engines are masterpieces in their own right but which engine gives the greatest aural sensation? The 458. The noise, the drama and the sheer excitement of the NA 4.5 V8 of the 458 is unmatched. A similar case can be presented for the Aventador's NA V12. Lamborghini, for now, has kept the drama of the V12 intact as it's clientele wanted that and were willing to pay for it.

So if NA engines really are such sought after, why is almost every manufacturer ditching them in favour of turbocharged engines? Ferrari is rumored to recreate it's old turbo magic by putting a rumored TT V8 in the successor to the 458 Italia. It has already put a turbo engine in the updated California. Bentley has adopted a TT V8 as well. Porsche has dumped it's NA engines in the Panamera S / Cayenne S and put in a turbo V6. The list goes on....

Why are we seeing this phenomena?

We need to approach this topic from a holistic viewpoint. First and foremost : Emission regulations are getting stricter and stricter and automobile manufacturers can either meet those emission standards or find themselves stuck with cars which cannot be sold. And what is the most fundamental way to improve emissions - by making the engine more efficient. A NA engine's biggest drawback is that it can take in air at a maximum of only atmospheric pressure. As the pressure varies, so does the capability to take in air. Hence you have instances of low power outputs in higher altitudes. Less air, less power, more effort used, more fuel used, less efficient, more emissions.

This is where the benefits of a turbocharger begin to show. A turbocharger is basically a fan to force air fitted to the intake of the car, so to speak. It can keep the intake at a predetermined pressure - say 5/10/20psi and hold it there, irrespective of the altitude. Now, two most important outcomes can be seen :

1. The engine can take in more air than it could have without the help of the turbo. More air means more fuel can be consumed and consequently more power can be made. Now how does it help efficiency and emissions then?
Simple - the NA engine is working harder than the Turbo one to be able to match the torque of the turbo engine - most NA engines are unable to match Turbo torque levels. Case in point : 1.4 FIRE vs 1.4 T-Jet. Since the NA engine is working harder, consequently it will be less efficient. You can ride the torque of the turbo engine at low rpm's and short shift the gears easily.

2. The engine can produce the same amount of power be it at sea level or high altitude. Since the turbo is acting as a compressor, it will work to maintain the same amount of preset pressure in the intake tract. The only difference being that the turbo will have to work harder at high altitude to compensate the drop in atmospheric pressure than at sea level. But hey, turbos are there to work hard, right?
So, the performance of a turbo engine stays relatively the same at high altitudes as it is at sea level.

As can be seen, manufacturers love turbos nowadays for very practical reasons and not merely emotional appeal.

On the other hand, if the intention is performance, a turbocharger is an engineer's best buddy. Who would have thought that a 1.5 litre 3 cylinder petrol engine can put out 231bhp and 320Nm torque (found in the BMW i8) if not for turbocharging? Or a merely 4 litre V8 putting out close to 600hp in the Audi RS7.

As I have attempted to highlight, be it by compulsion or by the prospect of high performance or by the intention of both - turbochargers are here to stay. The NA engine is at that point in history where either it will be relegated to super exotic status or be found in small lawn mowers motorcycles etc etc.

**The above are the musings of an idle Computer Engineer trying to act smart and write about a subject of Mechanical Engineering. Please discuss the mistakes so that we can all learn**.

Cheers.

I leave you with a photograph of the Twin-Turbo V8 masterpiece as found in the F10 M5. Note the turbos placed inside the V of the V8 : to maximise response and reduce lag.

The NA engine can make a nice sporty noise with the help of a good tuned exhaust. But a turbocharged engine cannot make too much of the sporty sounds as the velocity of the exhaust gases is converted to kinetic energy used to rotate the turbocharger. The result is that outgoing exhaust gases have very less energy left.

Coming to diesel engines in India, non-turbo engines are almost already history. But with petrol engines, it is still a long way to go I believe before turbo petrols will take over from the NA. Still the market is not open to turbo petrols (niche segment <10 lakhs as of now) with NA engines from Maruti, Hyundai and Honda ruling the roost. Once these companies enter the petrol turbo segment, this trend will stay for sure.

Turbo is the future, downsize the engine and add a turbo. Honda too has realised this and jumped into the bandwagon along with the Europeans. Wonder when Toyota will go Honda way for the Gasoline engines.

Maserati has managed to have a turbo charged engine as well as a sweet sounding exhaust.